1. Technical Field
This application relates to computer storage devices, and more particularly to the field of transferring data between storage devices.
2. Description of Related Art
Host processor systems may store and retrieve data using a storage device containing a plurality of host interface units (host adapters), disk drives, and disk interface units (disk adapters). Such storage devices are provided, for example, by EMC Corporation of Hopkinton, Mass. and disclosed in U.S. Pat. No. 5,206,939 to Yanai et al., U.S. Pat. No. 5,778,394 to Galtzur et al., U.S. Pat. No. 5,845,147 to Vishlitzky et al., and U.S. Pat. No. 5,857,208 to Ofek. The host systems access the storage device through a plurality of channels provided therewith. Host systems provide data and access control information through the channels to the storage device and the storage device provides data to the host systems also through the channels. The host systems do not address the disk drives of the storage device directly, but rather, access what appears to the host systems as a plurality of logical disk units. The logical disk units may or may not correspond to the actual disk drives. Allowing multiple host systems to access the single storage device unit allows the host systems to share data stored therein.
A significant number of mainframe applications that access tape drive data are still in use. In many cases, tape drives have been replaced by hardware and/or software that provides tape drive simulation/emulation. For example, the DLm960 device provided by EMC Corporation of Hopkinton, Mass. provides tape drive functionality so that applications in a host system coupled thereto (e.g., an IBM System z host device). Thus, applications running on a host system coupled to a DLm960 (or similar) would send tape commands and data thereto and receive tape data and status as if the applications were communicating with an actual tape drive. The DLm960 may include non-volatile storage (e.g., disk array) to store tape data and tape emulation information.
One issue associated with using tape emulation is that tape operation metadata may be stored separately from the tape data. For example, a host may maintain metadata (tape management data) such as tape retention time, tape ownership, tape security, etc. This metadata information may be stored in a storage device used by the host, such as a Symmetrix disk array storage device provided by EMC Corporation of Hopkinton, Mass. The tape data, on the other hand, may be stored in a separate storage device used for tape emulation. When both the tape information and the additional tape data are asynchronously transferred to a remote backup site to provide for disaster recovery, the metadata at the remote backup site is not necessarily synchronized with the tape data at the backup site since the asynchronous transfer of data from the different storage devices may be at different rates and/or cycle times. Thus, the additional tape data at the remote site may be inconsistent with the tape data at the remote site, making it difficult, if not impossible, to failover to the remote site in the case of a disaster at the primary site.
Accordingly, it is desirable to provide a tape emulation system that maintains consistency at a remote site between additional tape data and tape data when the data and metadata are transferred asynchronously to the remote site and are stored separately from each other.